Flame-resistant polycarbonates containing units deriving from halogenated carbonyl compounds in their polymer chain

ABSTRACT

Flame-resistant thermoplastic branched polycarbonates of high molecular weight are prepared from: 
     (1) a carbonate precursor; 
     (2) at least one dihydroxyaromatic compound of formula: ##STR1## where: R is a single bond, or a substituted or non-substituted linear or branched C 1  -C 5  alkylene radical, or a group chosen from O, S, SO 2  and CO; 
     X and Y, which may be the same or different, are H or CH 3  ; 
     m and n, which may be the same or different, are whole numbers from 1 to 4; 
     (3) at least one halogenated carbonyl compound of formula: ##STR2## where: Z is a group chosen from O, S, and NH; 
     R 1  and R 2 , which may be the same or different, are chlorine or bromine; 
     R is hydrogen or chlorine or bromine or a C 1  -C 3  alkyl radical; 
     p is zero or 1 or 2.

This invention relates to thermoplastic branched polycarbonates of highmolecular weight possessing flame-resistant properties(self-extinguishing).

Polycarbonates are known in the art for their excellent physical andmechanical properties such as their high impact strength and theirconsiderable dimensional and thermal stability.

Because of the continually increasing requirement for materials whichfor safety reasons possess not only excellent mechanical properties butalso flame-resistant properties, various methods have been devised inthe art for making polycarbonates self-extinguishing.

One of the most commonly used methods is based on introducing halogens,mainly bromine and chlorine, into the polycarbonate.

The halogens can be introduced into the polymer in the form of additivesby using generally polyhalogenated organic substances as described forexample in U.S. Pat. No. 3,357,942, if desired together with otheradditives of synergic action such as antimony oxide (J. T. Howarth etal., Plastic World, p. 64-74, March 1973).

It is also known to chemically bond the halogens to the polymer chain byusing bifunctional phenols such as tetrabromobisphenol A andtetrachlorobisphenol A as co-monomers in the preparation of thepolycarbonate (U.S. Pat. No. 3,334,154).

Halogenated substances of the known art, whether additives or monomersto incorporate in the polymer chain, must however be used in ratherlarge quantities to give the polycarbonate the requiredself-extinguishing properties.

Although the presence of large halogen quantities in the polycarbonateon the one hand makes the polymer able to resist the flame, on the otherhand it leads to degradation of the polycarbonate during its working, tothus cause deterioration in the physical and mechanical properties ofthe non-halogenated polycarbonate.

Moreover, the high temperatures necessary for working the polycarbonatecan cause degradation of the halogenated compounds, with release ofhydrohalogen acids and consequent damage to the machines by corrosion.

Thus the technical problem still unsolved is to produce polycarbonatespossessing flame-resistant properties which preserve all their inherentchemical, physical and mechanical properties intact.

It has now been found possible to solve said problem by preparingthermoplastic polycarbonates of high molecular weight possessingflame-resistant properties, by using a halogenated carbonyl compound asco-monomer in the preparation of the polycarbonate, said compound beingused in small quantities which are in any event less than such as wouldlead to undesirable changes in the polymer properties.

More particularly, according to the present invention, saidthermoplastic polycarbonates of high molecular weight possessingflame-resistant properties are prepared from:

(1) a carbonate precursor;

(2) at least one dihydroxyaromatic compound of formula: ##STR3## where:R is a single bond, or a substituted or non-substituted linear orbranched C₁ -C₅ alkylene radical, or a group chosen from O, S, SO₂ andCO;

X and Y, which may be the same or different, are H or CH₃ ;

m and n, which may be the same or different, are whole numbers from 1 to4;

(3) at least one halogenated carbonyl compound of formula: ##STR4##where: Z is a group chosen from O, S and NH;

R₁ and R₂, which may be the same or different, are chlorine or bromine;

R is hydrogen or chlorine or bromine or a C₁ -C₃ alkyl radical;

p is zero or 1 or 2.

For said polycarbonates to exhibit flame-resistant properties it issufficient for the molar ratio of (3) to (2) to be between 0.05/100 and5/100, and preferably between 0.5/100 and 3/100.

The following are some examples of dihydroxyaromatic compounds (I) whichcan be used:

4,4'-dihydroxydiphenyl

2,2-bis(4-hydroxyphenyl)propane (bisphenol A)

2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane;

bis(4-hydroxyphenyl)methane.

In addition to said dihydroxyaromatic compounds, compounds with a singlebivalent aromatic ring such as resorcin and hydroquinone can also beused.

The halogenated carbonyl compounds (3) can be prepared using knownmethods of organic chemistry.

For example, the compounds in which Z is NH can be prepared by reactingthe acid chloride of a carboxylic acid of formula ##STR5## where R andR₁ have the aforesaid meaning, with an aromatic amine of formula:##STR6## where R₂ and p have the aforesaid meaning, by conducting thereaction in an organic solvent such as dioxane or acetone at atemperature of the order of 50°-120° C. and using a molar amine/acidchloride ratio which is double the stoichiometric so that the evolvinghydrochloric acid reacts with the excess amine.

The other halogenated carbonyl compounds can be prepared in similarmanner using suitable reactants.

Some examples of halogenated carbonyl compounds suitable for thepurposes of the present invention are:

N-(p'-hydroxyphenyl)-2,2-dichloroacetamide;

N-(p-hydroxyphenyl)-2-chloroacetamide;

N-(2'-hydroxy-5'-chlorophenyl)-2,2-dichloroacetamide;

N-(4'-hydroxy-2',6'-dichlorophenyl)-dichloroacetamide;

S-(p-hydroxyphenyl)-2,2-dichlorothioacetate;

S-(p-hydroxyphenyl)-2-chlorothioacetate;

p-hydroxyphenyl-2,2-dichloroacetate;

p-hydroxyphenyl-2-chloroacetate;

The carbonate precursor can be phosgene or a chloroformyl-terminatedpolycarbonate oligomer (MW between 400 and 2000) prepared by reactingphosgene with a dihydroxyaromatic compound of formula I, or it can be adiaryl, dialkyl or alkylaryl ester of carbonic acid, such as diphenylcarbonate.

The flame-resistant polycarbonates prepared from the aforesaid compounds(1), (2) and (3) have a linear structure. However, the flame-resistantproperties can be enhanced if branching is provided in thepolycarbonate.

This branching can be obtained by using a polyfunctional organiccompound as branching agent in addition to said compounds (1), (2) and(3).

Polyfunctional organic compounds for use as branching agents arecompounds known in the art and are characterised by possessing at leastthree equal or different functional groups chosen from the groups OH,COOH, COCl and SO₂ Cl.

For example, the branching agents used can be those compounds describedin Italian Patent Applications N. 23538 A/84, 20927 A/87 and U.S. Pat.Nos. 4,857,628, 4,789,723, 4,786,707, 4,788,273, 4,798,882 and patentapplication Ser. Nos. 203,705, 204,425.

The following polyfunctional organic compounds are particularlypreferred for the purposes of the present invention:

2,4,6-tris(4'-hydroxyphenyl)amino-s-triazine;

3,7-dihydroxy-β-naphthoic acid;

1,3,5-trihydroxybenzene;

4,4'-methylenebis(3-hydroxy-2-carboxynaphthalene);

tris(4-hydroxyphenyl)methane;

2,3,4,5-tetrachlorocarbonyltetrahydrofuran;

1,3,6-trichlorosulphonylnaphthalenic acid;

The quantity of branching agent used is such that the the molar ratio ofthe branching agent to the compound (2) is between 0.01/100 and 5/100.

The flame-resistant polycarbonates of the present invention can beprepared by reacting together, in accordance with one of thepolymerization methods usually used to produce polycarbonates, (1) acarbonate precursor, (2) a dihydroxyaromatic compound of formula I, (3)a halogenated carbonyl compound of formula II, the molar ratio of (3) to(2) varying from 0.05/100 to 5/100.

The polycarbonates obtained in this manner have a linear structure; if abranched structure is to be obtained, a polyfunctional organic compoundas branching agent must be added in a quantity such that the molar ratioof branching agent to compound (2) is between 0.01/100 and 5/100.

One of the polymerization method which can conveniently be used forpreparing the polycarbonates of the present invention is interfacialpolycondensation. In this method, the dihydroxyaromatic compound (2) andthe halogenated carbonyl compound (3) are dissolved in an aqueous sodiumhydroxide solution and an organic solvent immiscible with water such asmethylene chloride is then added to this mixture.

Phosgene gas is then bubbled through the obtained mixture in thepresence of a phase transfer catalyst such as triethylamine, and thereaction is maintained at a temperature of between 15° and 25° C. for aperiod of between 20 minutes and 6 hours.

According to a preferred embodiment of the present invention, thepolycarbonates can be prepared using as carbonate precursorschloroformyl-terminating polycarbonate oligomers, which can be preparedby interfacial reaction between phosgene and a dihydroxyaromaticcompound of formula I, in the presence of a molecular weight regulatorsuch as tert.butylphenol.

In practice, said chloroformyl-terminating oligomers, the molecularweight of which varies from 400 to 2000, are dissolved in awater-immiscible organic solvent and are then reacted, again by theinterfacial polycondensation method, with compounds (2) and (3) inaqueous alkaline solution, in the presence of a phase transfer catalyst.

As an alternative to interfacial polycondensation, the polycarbonates ofthe present invention can be prepared by the known method ofpolycondensation in solution.

In this case, phosgene is bubbled through a solution of methylene andpyridine containing the dihydroxyaromatic compound (2) and thehalogenated carbonyl compound (3).

It is also possible to prepare said polycarbonates bytransesterification in the molten state, by reacting carbonic aciddialkyl, diaryl or alkylaryl esters as carbonate precursors with thedihydroxyaromatic compound (2) and the halogenated carbonyl compound (3)at a temperature of between 100° and 300° C. in the presence oftransesterification catalysts.

The polycarbonates prepared by any of the aforesaid methods have aprevalent molecular weight of between 20,000 and 30,000; they preserveall the inherent characteristics of thermoplastic materials intact. Saidpolycarbonates can be classified as V-0 in their fire behaviour,evaluated by the UL94 code (underwriters' Laboratories Inc., bulletinS4) and conducted on test pieces of 3.2 mm thickness prepared bycompression or injection.

According to said code the materials are classified V-0, V-1 or V-2based on the results obtained in five tests, in accordance with thefollowing criteria:

V-0: No test piece must show a combustion time exceeding 30 secondsafter removal of a bunsen flame. The total combustion time for the fivetest pieces (ten ignitions) must not exceed 250 seconds. No test piecemust allow burning particles to drip and ignite surgical cotton placedvertically under the test piece at a distance of 305 mm.

V-1: No test piece must show a combustion time exceeding 30 secondsafter removal of a bunsen flame. The total combustion time for the fivetest pieces (ten ignitions) must not exceed 250 seconds. No test piecemust allow burning particles to drip and ignite surgical cotton placedvertically under the test piece at a distance of 305 mm.

V-2: No test piece must show a combustion time exceeding 30 secondsafter removal of a bunsen flame. The total combustion time for the fivetest pieces (ten ignitions) must not exceed 250 seconds. The test piecesmay allow burning particles to drip and ignite surgical cotton placedvertically under the test piece at a distance of 305 mm.

In addition all five test pieces must pass the test prescribed by UL-94otherwise they are classified on the basis of the behaviour of the worsttest piece. For example, if one test piece shows V-2 behaviour whereasthe other four show V-0 behaviour, all five test pieces are classifiedV-2. Finally, if a test piece continues to burn for more than 30 secondsafter removing the bunsen flame, it cannot be classified under UL-94 butinstead is indicated as a flammable test piece.

The test pieces are also subjected to a fire-behaviour test inaccordance with ASTM D 2863-77 which correlates the flammability of apolymer material with the oxygen concentration of the atmosphere inwhich the test piece is located. This correlation is expressed by theLOI (limiting oxygen index), i.e. the minimum oxygen percentage able tomaintain combustion of the test piece in the oxygen-nitrogen atmospherewhich flows about the test piece from the bottom upwards.

The following characteristics were also determined on the polycarbonatesof the present invention:

Intrinsic Viscosity (η)

This property is determined in methylene chloride at 20° C. by anUbbelhode viscometer and is expressed in dl/g.

Melt Flow Index (MFI)

The melt flow index is evaluated in a melt indexer on an extrudedgranulate, under a load of 1.2 kg at a temperature of 300° C., inaccordance with ASTM D1238.

Impact Strength (IZOD)

This is evaluated on notched test pieces at 0° C. in accordance withASTM D256.

Shear Sensitivity (SS)

This quantity is evaluated in a melt indexer on an extruded granulate,under loads of 1.2 and 12 kg at a temperature of 300° C., in accordancewith ASTM D1238.

The following experimental examples are given for illustrative purposesonly and are not to be taken as limitative of the scope of theinvention.

EXAMPLE 1 Preparation of N-(p-hydroxyphenyl)-2,2-dichloroacetamide (informula II: Z is NH; R and R₁ are chlorine; p is zero)

22.7 g (208 mmoles) of p-aminophenol dissolved in 100 ml of dioxane areplaced in a 250 ml 4-neck flask fitted with a mechanical stirrer,thermometer and reflux condenser, operating under an inert gasatmosphere.

15.3 g (104 mmoles) of dichloroacetylchloride dissolved in 20 ml ofdioxane are added, and the resultant mixture is left for 1 hour at 100°C.

On termination of this period, the precipitated p-aminophenolhydrochloride is filtered off and the resultant solution poured into 4liters of n-hexane.

The product which precipitates is separated by filtration and dried inan oven under vacuum at 100° C. for 4 hours.

In this manner 21 g of N-(p-hydroxyphenyl)-2,2-dichloroacetamide areobtained with a yield of 92%.

The product had the following characteristics:

Melting point (DSC): 134° C.

Equivalent weight (acidimetric): 217 (theoretical=220)

    ______________________________________                                        Elementary analysis:                                                                       C    H         N     Cl                                          ______________________________________                                        Experimental % 43.7   3.2       6.2 31.78                                     Theoretical %  43.7   3.2       6.4 31.2                                      ______________________________________                                    

The product structure was confirmed by NMR spectroscopic analysis.

EXAMPLE 2

84 g of bisphenol A, 65.2 g of sodium hydroxide and 2.4 g ofN-(p-hydroxyphenyl)-2,2-dichloroacetamide (3.0 mol % on the bisphenol A)dissolved in 650 ml of water, 20 mg of sodium dithionate (as reducingagent to prevent the formation of coloured by-products) and 6.3 ml of a0.5N aqueous triethylamine solution are fed under nitrogen into a 3liter glass reactor temperature-controlled at 25° C.

1300 ml of methylene chloride are then added and 44 g of phosgene gasare bubbled over a time of 30 minutes through the mixture, which issubjected to vigorous stirring.

The reaction proceeds for 2 hours, aqueous sodium hydroxide (20 wt %)being added to keep the pH continuously greater than 11.

The mixture is then diluted with 500 ml of methylene chloride and theorganic phase is separated and washed successively with 300 ml of water(twice), 800 ml of 0.15N sodium hydroxide (3 times), 600 ml of water(twice) and 800 ml of 0.1N hydrochloric acid and finally with 600 mlportions of water until neutral.

The polymer is finally recovered by distilling off the organic solventand is dried and ground to obtain a powder.

The polycarbonate obtained in this manner is then extruded at 260° C.and the extrusion cooled and granulated.

The granules are moulded either by compression (285° C., 40 kg/cm²) orby injection (300° C.) to obtain test pieces of size 127×6.5×3.2 mm.

Five test pieces are subjected to the fire behaviour test described inUL 94. They are found to be V-0, in accordance with the data given inTable 1.

The other polycarbonate characteristics are given in Table 2.

EXAMPLE 3

Example 2 is repeated using the same operating method and reactantquantities, with the exception that 2.7 g of p-tert.butylphenol areadded and no halogenated carbonyl compound is used.

The polycarbonate obtained is found to be V-2 at the fire behaviourtest, in accordance with UL 94 (see Table 1).

The other polymer characteristics are given in Table 2.

EXAMPLE 4

253.8 g of polycarbonate chloroformyl-terminating oligomers (averagemolecular weight 681, chloroformyl terminal groups=2758 meq/kg, hydroxylterminal groups=180 meq/kg) prepared from bisphenol A and phosgene anddissolved in 900 ml of methylene chloride and fed under nitrogen into aglass reactor of 2.5 liters capacity temperature controlled at 25° C.

To the solution, mechanically stirred by a double-anchor device (300RPM) are then added, in the stated order, 50 ml of water containing 6.2g of N-(p-hydroxyphenyl)-2,2-dichloroacetamide (equal to 2.4 mol % onthe bisphenol A), 1.5 g of caustic soda, 31 mg of sodium dithionate and7 ml of an aqueous 0.05N triethylamine solution.

After 40 minutes 350 ml of water are added containing 65.9 g ofbisphenol A, 24.0 g of caustic soda and 31 mg of sodium dithionate.

115 ml of a 20 wt % aqueous caustic soda solution are then added over aperiod of 10 minutes using a metering pump.

After 3 hours the reaction mixture is poured into 2200 ml of methylenechloride; the organic phase is then separated and washed, in the statedorder, with 900 ml of water (twice), 1300 ml of 0.15N aqueous sodiumhydroxide (3 times), 900 ml of water (twice) and 1300 ml of 0.1Nhydrochloric acid, and finally with 900 ml portions of water untilneutral.

The polymer is recovered by distilling off the organic solvent, and isdried and ground to obtain a powder.

The polycarbonate obtained in this manner is then extruded at 260° C.and the extrusion cooled and granulated.

The granules are moulded by injection or compression to obtain testpieces of size 127×6.5×3.2 mm.

Five test pieces are subjected to the fire behaviour test described inUL 94 and are found to be V-0, in accordance with the data given inTable 1.

The other polycarbonate characteristics are given in Table 2.

EXAMPLE 5

Example 4 is repeated using the same operating method and reactantquantities, except that 7.7 g ofN-(p-hydroxyphenyl)-2,2-dichloroacetamide (3 mol % on the bisphenol A)are added.

The polycarbonate obtained is found to be V-0 at the fire behaviourtest, evaluated in accordance with UL 94.

The test results are given in Table 1.

The other polymer characteristics are given in Table 2.

EXAMPLE 6

Example 5 is repeated using the same operating method and reactantquantities, except that 1.71 g of 2,4,6-tris(4-hydroxyphenyl)amino-s-triazine (equal to 0.36 mol % on the bisphenol A) are alsoadded.

The polycarbonate obtained is found to be V-0 at the fire behaviourtest, evaluated in accordance with UL 94.

The test results are given in Table 1.

The other polycarbonate characteristics are given in Table 2.

EXAMPLE 7

Example 4 is repeated using the same operating method and reactantquantities, except that 5.3 g of p-tert.butylphenol are added and nohalogenated carbonyl compound is added.

The polycarbonate obtained is found to be V-2 at the fire behaviourtest, evaluated in accordance with UL 94.

The test results are given in Table 1.

The other polycarbonate characteristics are given in Table 2.

                  TABLE 1                                                         ______________________________________                                             Total combustion time                                                                        Maximum combustion                                                                           Classifi-                                       of 5 test pieces (10                                                                         time per test piece                                                                          cation                                     Ex.  ignitions (seconds)                                                                          (2 ignitions) (seconds)                                                                      UL-94                                      ______________________________________                                        2    35              8             V-0                                        3    112            25             V-2                                        4    33             10             V-0                                        5    23              7             V-0                                        6    19              5             V-0                                        7    107            23             V-2                                        ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                             [η] 20° C.                                                                         Impact                                                        CH.sub.2 Cl.sub.2                                                                      LOI    (IZOD) MFI (300° C.;                                                                    SS (300° C.;                     Ex.  (dl/g)   %      (J/m)  1.2 kg)   1.2 & 12 kg)                            ______________________________________                                        2    0.507    31     783    8.5       12.8                                    3    0.518    26     724    8.0       13.1                                    4    0.571    31     763    4.2       12.7                                    5    0.493    32     721    9.0       13.3                                    6    0.551    35     792    5.1       23.1                                    7    0.502    27     744    8.7       12.9                                    ______________________________________                                    

We claim:
 1. A thermoplastic polycarbonate of high molecular weightpossessing flame-resistant properties, produced from:(1) a carbonateprecursor; (2) at least one dihydroxyaromatic compound of formula:##STR7## where R is a single bond, or R is a substituted ornon-substituted linear or branched C₁ -C₅ alkylene radical, or isselected from the group consisting of O, S, SO₂ and CO; X and Y, whichare the same or different, are H or CH₃ ; m and n, which are the same ordifferent, are whole numbers from 1 to 4; (3) at least one halogenatedcarbonyl compound of the formula ##STR8## where: Z is selected from thegroup consisting of O, S and NH;R₁ and R₂, which are the same ordifferent, are chlorine or bromine; R is hydrogen or chlorine or bromineor a C₁ -C₃ alkyl radical; and p is zero, 1 or
 2. 2. A polycarbonate asdefined in claim 1, wherein the molar ratio of (3) to (2) is between0.05/100 and 5/100.
 3. A polycarbonate as defined in claim 2, whereinthe molar ratio of (3) to (2) is between 0.5/100 and 3/100.
 4. Apolycarbonate as defined in claim 1, wherein the carbonate precursor isselected from the group consisting of phosgene, chloroformyl-terminatingpolycarbonate oligomers having a molecular weight of between 400 and2000, and carbonic acid diaryl, dialkyl and arylalkyl esters.
 5. Apolycarbonate as defined in claim 1, wherein the dihydroxyaromaticcompound (2) is selected from the group consisting of:4,4'-dihydroxydiphenyl; 2,2-bis(4-hydroxyphenyl)propane;2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane; andbis(4-hydroxyphenyl)methane.
 6. A polycarbonate as defined in claim 1,wherein the halogenated carbonyl compound (3) is selected from the groupconsisting of:N-(p-hydroxyphenyl)-2,2-dichloroacetamide;N-(p-hydroxyphenyl)-2-chloroacetamide;N-(2'-hydroxy-5'-chlorophenyl)-2,2-dichloroacetamide;S-(p-hydroxyphenyl)-2,2-dichlorothioacetate;S-(p-hydroxyphenyl)-2-chlorothioacetate;p-hydroxyphenyl-2,2-dichloroacetate; andp-hydroxyphenyl-2-chloroacetate.
 7. A method for preparing apolycarbonate as defined in claim 1, comprising reacting together (1) acarbonate precursor, (2) a dihydroxyaromatic compound of formula (I),and (3) a halogenated carbonyl compound of formula (II), wherein themolar ratio of (3) to (2) varies from 0.05/100 to 5/100.
 8. A method asdefined in claim 7, wherein the carbonate precursor is selected from thegroup consisting of phosgene, chloroformyl-terminating polycarbonateoligomers having a molecular weight between 400 and 2000, and carbonicacid diaryl, dialkyl and arylalkyl esters.
 9. A method as defined inclaim 7, wherein the carbonate precursor is a chloroformyl-terminatingpolycarbonate oligomer.